1. Field of the Invention
The present invention relates generally to offshore drilling structures and, more specifically, to anti-fouling ion injection systems/methods for offshore drilling structures.
2. Description of the Background
Various types of marine fouling exist, ranging from bacteria and fungi, to free swimming animal larvae. Once the larvae are allowed to enter and adhere to the interior walls of the sea water system, they begin to grow and colonize. If this natural process goes unchecked, a partial or complete blockage in the seawater piping is inevitable. The uncontrolled growth of marine fouling organisms restricts flow, creates turbulent fluid flow, reduces pressure, and causes the motor to overheat. Many cases have been reported where marine fouling has caused major damage to seawater pump systems.
Marine growth fouling in seawater pumping systems for offshore drilling structures is the cause of many operational problems. For instance, problems may include reduced pump life due to clogged intake areas, accelerated corrosion on metal surfaces after barnacles attach, compromised downstream equipment due to restricted piping manifolds, and the need for frequent cleaning of caissons, piping, and strainers. By protecting against fouling, operating and maintenance costs are reduced and the life of the offshore equipment is protected.
Alternative methods are available to combat marine growth fouling, with the most common being chlorination. Typical ways to introduce chlorine into the sea water system are Chlorine Gas Injection, Hypochlorite Injection, and In-situ production of Hypochlorite by electrolysis of seawater. However, chlorination systems involve high capital outlays. As well, the operating and maintenance costs of chlorination systems are high. Furthermore, chlorine treatment systems have additional problems such as toxicity, corrosiveness, and safety hazards.
The following prior art discloses patents that attempt to solve the above and/or related problems:
U.S. Pat. No. 6,852,235, issued Feb. 8, 2005, to Holland, discloses a method and apparatus that provide fluid treatment at a plurality of distinct points using a length of energized magnetically conductive conduit in fluid communication with non-magnetic coupling devices. The instant invention prevents the formation and accumulation of contaminants within conduits and on equipment utilized in the transportation, delivery and processing of fluid columns. It may also be utilized to accelerate the separation of oil and water and increase the efficiency of oil/water separation equipment.
U.S. Pat. No. 6,730,205, issued May 4, 2004, to Holland, discloses a method and apparatus for the treatment of fluid columns that uses an air-cooled electromagnetic field generator to prevent the deposition and accumulation of contaminants within conduits and on equipment utilized in the transportation, delivery and processing of the fluid columns. The instant invention may be utilized to accelerate the separation of oil and water and increase the efficiency of such separation apparatus.
U.S. Pat. No. 6,267,979, issued Jul. 31, 2001, to Raad et al, discloses control of biofouling in pipes or aqueous systems via the use of compositions and methods that include the combination of a chelator with an antimicrobial agent.
U.S. Pat. No. 6,244,346, issued Jun. 12, 2001, to Perriello, discloses a method and apparatus in which alkane-utilizing bacteria are used to reduce fouling of injection and recovery wells. Fouling materials such as combinations of bacteria and metal oxides that would otherwise clog the wells are prevented from depositing on the wells. In a preferred embodiment, a butane substrate and an oxygen-containing gas are injected near a well inlet or outlet to stimulate the growth of butane-utilizing bacteria which are effective at reducing or eliminating fouling of the well.
U.S. Pat. No. 6,183,646, issued Feb. 6, 2001, to Williams et al, discloses the reduction and prevention of biofouling in facilities utilizing water, e.g. sea water, carrying biological organisms, without causing corrosion, chemical reaction or other detrimental action from the additive or environmental discharge problems. Such operations include, for example, desalination plants, power plants, oilfield water injection facilities and shipboard or ocean platform fire water systems. For example, in the desalination plant of FIG. 1, the biofouling reduction method and apparatus for this invention have a source of oxidizing agent such as chlorine ions or ozone, a source of copper ions and a dosing chamber for delivery of relatively low dosage levels of oxidizing agents and at appropriate times copper ions to form a treatment additive. Flow connectors connect the dosing chamber to various points along the piping in the desalination plant. A controller controls the operation of the dosing chamber and valves along the flow connectors to operate in a sequential target dosing mode to deliver treatment additive of predetermined composition to selected points along the piping at predetermined times and in predetermined concentrations.
U.S. Pat. No. 5,998,200, issued Dec. 7, 1999, to Bonaventura et al, discloses a method for preventing fouling of an aquatic apparatus by an aquatic organism which comprises affixing a biologically active chemical to a surface intended for use in contact with an aquatic environment containing the organism, wherein the chemical is an enzyme, repellant, chelating agent, enzyme inhibitor, or non-metallic toxicant capable of hindering the attachment of the organism to the surface while affixed to the surface, along with improved apparatuses which are produced using the method.
U.S. Pat. No. 5,616,250, issued Apr. 1, 1997, to Johnson et al, discloses an improved system and novel components and methods for treating waste waters contaminated with a variety of commercial, municipal, and/or industrial contaminants. A mixing vessel according to the invention comprises upper and lower mixing chambers connected by an intermediate tubular section and a fluid exit tube running coaxially down the center of the intermediate tubular portion. The fluid stream to be treated flows in a spiral pattern vertically through the vessel, providing turbulent flow. The flow stream may be subjected to electric or magnetic fields. In one embodiment, streams of the fluid to be treated and of an ionized coagulant are combined prior to entry into the vessel; in another embodiment, the incoming flow stream is combined with the coagulants in the mixing vessel. The incoming flow may be split between annular passageways to improve mixing. Magnetite particles may be generated in situ and added to the flow stream to further encourage coagulation in the presence of a magnetic field. After exiting the mixing chamber, the coagulated contaminants may be removed using a variety of filtration steps.
U.S. Pat. No. 4,988,444, issued Jan. 29, 1991, to Applegate et al, discloses an improved process for killing and inhibiting growth and reproduction (after-growth) of microorganisms comprising adding sufficient chloramine to kill the microorganisms without oxidizing high molecular weight organics, which are not easily assimilated by organisms that survive, into lower molecular weight ones, which are easily assimilated.
U.S. Pat. No. 4,869,016, issued Sep. 26, 1989, to Diprose et al, discloses a method to provide a substantial reduction of marine corrosion in sea water by micro and macro biofouling. An alternating current is generated of a strength and frequency sufficient to shock marine biofouling organisms and sufficient to upset the normal behavior patterns of the marine biofouling organisms entrained in the sea water passing around or through the structure. A second combination of alternating and direct currents are generated between two strategically located electrodes whereby to release into the water around or within the structure controlled amounts of chlorine ions and copper ions to produce an environment actively hostile to potential marine biofouling organisms. The effect of releasing copper ions and chlorine ions simultaneously is that they co-operate in a synergistic manner that greatly enhances the biocidal effect on marine organisms over and above the effect of the separate use of copper ions and chlorine ions.
U.S. Pat. No. 4,776,384, issued Oct. 11, 1988, to Kawabe et al, discloses a method of monitoring the inner surfaces of copper-alloy condenser tubes of a condenser through which seawater flows as a coolant by controlling a ferrous-ion injecting operation to inject ferrous ions into the coolant for forming a protective film on the inner surfaces of the condenser tubes, and a sponge-ball cleaning operation to clean the inner tube surfaces by passing sponge balls through the condenser tubes. During an initial period of exposure of the condenser tubes to the coolant after installation of the condenser tubes in the condenser, the ferrous ions are injected into the coolant to form the protective film on the inner surfaces of the condenser tubes. Subsequently, the ferrous-ion injecting operation and the sponge-ball cleaning operation are executed while the polarization resistance and heat transfer rate of the condenser tubes are monitored. The injecting and cleaning operations are performed to maintain within suitable ranges the polarization resistance and the heat transfer rate of the condenser tubes. These ranges may vary, depending upon whether the coolant is non-chlorinated seawater, chlorinated seawater, or sulfide-ion polluted seawater.
U.S. Pat. No. 3,984,302, issued Oct. 5, 1976, to Freedman et al, discloses that marine fouling of the tubes of heat exchangers, piping conduits, and like apparatus through which sea water flows is controlled with the aid of an assembly mounted in situ within the system at the inlet ends of the tubes which generates chlorine gas by electrolytic action. The chlorine gas is distributed by the flowing sea water through the tubes and prevents the accumulation of marine plant and animal material on the internal surface of the tubes, thus controlling marine fouling.
The above cited prior art does not provide a solution to the aforementioned problems. Because those skilled in the art have recognized and attempted to solve these problems in the past, they will appreciate the present invention, which addresses these and other problems.